The present disclosure relates generally to wellbore equipment and, more specifically, to a field adjustable impact jar.
In oil and gas well operations, a work string or portions thereof may become lodged within a wellbore to such a degree that it cannot be readily dislodged. Consequently, it is frequently necessary to inflict axial blows to lodged or securely installed equipment to attempt its removal.
A jar is one type of device often employed in wellbore operations to enable the delivery of such axial blows. Generally, a jar includes anvil and hammer portions configured such that sliding the hammer and anvil together at high velocity imparts an impact force or impulse (hereafter collectively referred to as either an impact force, an impulse or an impulse force) to the lodged equipment, hopefully sufficient to dislodge the lodged equipment. A triggering mechanism is typically employed to retard or delay the motion of the anvil and hammer relative to each other until the working string experiences a predetermined amount of axial tensile strain. The axial tensile strain is caused by a tensile load applied at the well surface by a wireline or another portion of a working string. This tensile force is resisted by the triggering mechanism of the jar long enough to allow the working string to stretch and store potential energy. When the jar triggers, the stored potential energy is converted to kinetic energy causing a high impulse impact between the anvil and hammer portions.
Operation of such impact jars may be hydraulic, mechanical or a combination thereof. A mechanical jar usually includes a friction sleeve coupled to the mandrel to resist movement of the mandrel until the tensile load exceeds a predetermined amount. A hydraulic jar has an orifice within it and is filled with a liquid. It is operated by building tension on the working string or tool string and waiting for sufficient fluid to bypass internally to allow the jar to reach its internal release position. The jar then rapidly opens such that stored energy is imparted to the lodged equipment.
Mechanical jars and hydraulic jars each have advantages over the other. Mechanical jars must be adjusted on the surface to the anticipated release tension prior to being run in the hole. If these jars are set to a release tension which cannot be attained upon down-hole engagement, or if the tension proves to be too low to be effective, the work string must be disengaged, pulled out of the hole, and readjusted.
Hydraulic jars also offer a wide variety of possible triggering loads. The range of possible triggering loads for a hydraulic jar is a function of the amount of axial strain applied by stretching the working string, and is limited only by the structural limits of the jar and the seals therein. However, hydraulic jars are also relatively expensive and not very dependable, as they have a tendency to become contaminated by wellbore environments due to the high internal temperatures and pressure differentials inherent to their operation. Most hydraulic jars are also relatively long, in some instances having a length exceeding 25 feet.
Working strings suspend tool strings in the wellbore via e-lines, slicklines, coiled tubing, snubbing or combinations thereof. Generally, e-lines employ a multi-functional wire to suspend a tool in a specific location in a well and to transmit power and/or data signals between the wellbore and the well surface. Conversely, slicklines employ a simple or braided wire to suspend a tool in its selected location, and are designed to require no electrical power from the surface to perform their designed function. Coiled tubing generally comprises continuous pipe or tubing stored on a tubing reel, whereas snubbing generally comprises jointed pipe or tubing assembled at the surface before insertion. Some operations may include both e-line and slickline applications, or other combinations, thereby necessitating pulling the working string from the wellbore to interchange tools before running the working string back into the wellbore. Obviously, this change is deleterious to the efficiency and productivity of wellbore operations.
Accordingly, what is needed in the art is an impact jar that addresses the above-discussed issues.